U.S. patent application number 13/636600 was filed with the patent office on 2013-01-24 for mainstream wastewater treatment.
This patent application is currently assigned to SEVERN TRENT WATER PURIFICATION, INC.. The applicant listed for this patent is Donald McCarty. Invention is credited to Donald McCarty.
Application Number | 20130020257 13/636600 |
Document ID | / |
Family ID | 44673661 |
Filed Date | 2013-01-24 |
United States Patent
Application |
20130020257 |
Kind Code |
A1 |
McCarty; Donald |
January 24, 2013 |
Mainstream Wastewater Treatment
Abstract
One or more embodiments of the present invention relate to a
short cut or shortened method for the removal of nitrogen from
wastewater by pairing an aerobic fixed-film biological reactor with
an anoxic fixed-film biological reactor under unique operating
conditions.
Inventors: |
McCarty; Donald;
(Elizabethtown, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
McCarty; Donald |
Elizabethtown |
PA |
US |
|
|
Assignee: |
SEVERN TRENT WATER PURIFICATION,
INC.
Colmar
PA
|
Family ID: |
44673661 |
Appl. No.: |
13/636600 |
Filed: |
March 25, 2011 |
PCT Filed: |
March 25, 2011 |
PCT NO: |
PCT/US11/30029 |
371 Date: |
October 3, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61318022 |
Mar 26, 2010 |
|
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|
Current U.S.
Class: |
210/614 ;
210/150; 210/620; 210/622; 210/630; 210/96.1 |
Current CPC
Class: |
Y02W 10/15 20150501;
C02F 2209/06 20130101; C02F 2209/14 20130101; C02F 3/302 20130101;
C02F 2209/07 20130101; C02F 3/104 20130101; C02F 2209/006 20130101;
Y02W 10/10 20150501; C02F 2209/16 20130101; C02F 2209/008 20130101;
C02F 3/2806 20130101; C02F 2209/18 20130101; C02F 2209/22 20130101;
C02F 2209/15 20130101; C02F 3/308 20130101; C02F 3/006
20130101 |
Class at
Publication: |
210/614 ;
210/620; 210/630; 210/622; 210/150; 210/96.1 |
International
Class: |
C02F 3/02 20060101
C02F003/02; C02F 3/30 20060101 C02F003/30 |
Claims
1. A method for removing nitrogen from wastewater rich in
ammonium-nitrogen comprising: directing a mainstream of the
wastewater to a first-stage reactor, the first-stage reactor
comprising an aerobic treatment zone; operating a control system
for short circuiting a conventional nitrification pathway in the
first-stage reactor, the short circuiting facilitating partial
oxidation of the ammonium-nitrogen in the mainstream to nitrites;
and denitrifying the nitrites by conveying an effluent comprising
the nitrites from the first-stage reactor to a second-stage
reactor, the second-stage reactor inoculated with heterotrophic
denitrifying microorganisms, the denitrification achieving total
nitrogen levels substantially less than 5 mg/L.
2. The method of claim 1, the first-stage reactor further
comprising one or more anoxic treatment zones.
3. The method of claim 2, the operating the control system further
comprising creating an environment in the aerobic treatment zone
that is conducive to short circuiting the conventional
nitrification pathway by facilitating growth of ammonia oxidizing
bacteria and inhibiting growth of nitrite oxidizing bacteria.
4. The method of claim 3, the operating the control system further
comprising: controlling levels of dissolved oxygen in the
mainstream to create the environment conducive to short circuiting,
the controlling dissolved oxygen levels further comprising:
receiving input values for one or more process parameters to
generate at least one set point value for the one or more process
parameters, the one or more process parameters affecting the short
circuiting; calculating an initial factor corresponding to a
percent of time for intermittently applying a fixed rate of process
air to the first-stage reactor to create the conducive environment;
sampling the mainstream to measure the one or more process
parameters; and comparing the measured process parameters against
the set point values and the calculated initial factor to regulate
an intermittent application of the process air to the first-stage
reactor.
5. The method of claim 4, the controlling dissolved oxygen levels
further comprising introducing controlled amounts of dissolved
oxygen to the first-stage reactor.
6. The method of claim 5, the introducing controlled amounts of
dissolved oxygen to the first-stage reactor further comprising
intermittently applying a fixed rate of process air to the
first-stage reactor.
7. The method of claim 5, the operating the control system further
comprising introducing controlled amounts of a carbon source to the
second-stage reactor.
8. The method of claim 4, the one or more process parameters
further comprising wastewater flow, ammonium, ammonium-nitrogen,
ammonia, ammonia-nitrogen, nitrates, nitrate-nitrogen, nitrites,
nitrite-nitrogen, chemical oxygen demand, biochemical oxygen
demand, carbonaceous biochemical oxygen demand, dissolved oxygen,
pH, alkalinity, geometry of the first-stage reactor, and geometry
of the second-stage reactor.
9. The method of claim 1, further comprising controlling pH levels
in the first-stage reactor to about 8.3, the pH level control
further comprising: introducing alkaline feedstock to the
first-stage reactor and/or recycling a denitrified effluent from
the second-stage reactor to the first-stage reactor.
10. The method of claim 1, further comprising maintaining anoxic
conditions in the second-stage reactor for facilitating reduction
of the nitrites in the effluent to nitrogen gas.
11. The method of claim 1, the denitrified effluent exiting the
second-stage reactor comprising total phosphorous levels less than
0.3 mg/L.
12. A system for removing nitrogen from wastewater rich in
ammonium-nitrogen comprising: a mainstream treatment system
comprising: a first-stage reactor, the first-stage reactor
comprising an aerobic treatment zone; a control system, the control
system facilitating a short circuiting of a conventional
nitrification pathway in the first-stage reactor, the short
circuiting partially oxidizing ammonium-nitrogen in the mainstream
to nitrites; and a second-stage reactor, wherein an effluent
comprising nitrites is conveyed from the first-stage reactor to the
second-stage reactor for denitrification, the second-stage reactor
inoculated with heterotrophic denitrifying microorganisms, the
denitrification achieving total nitrogen levels substantially less
than 5 mg/L.
13. The system of claim 12, the first-stage reactor further
comprising one or more anoxic treatment zones.
14. The system of claim 13, the first-stage reactor further
comprising an environment in the aerobic treatment zone that is
conducive to short circuiting the conventional nitrification
pathway by facilitating growth of ammonia oxidizing bacteria and
inhibiting growth of nitrite oxidizing bacteria.
15. The system of claim 14, the control system comprising a
computer control system, the control system further comprising: a
computer program stored on a non-transitory storage medium, the
computer program including instructions configured to be executed
on the computer control system to perform a method for controlling
levels of dissolved oxygen in the mainstream to create the
environment conducive to short circuiting, the controlling
dissolved oxygen levels further comprising: receiving input values
for one or more process parameters to generate at least one set
point value for the one or more process parameters, the one or more
process parameters affecting the short circuiting; calculating an
initial factor corresponding to a percent of time for
intermittently applying a fixed rate of process air to the
first-stage reactor to create the conducive environment; sampling
the mainstream to measure the one or more process parameters; and
comparing the measured process parameters against the set point
values and the calculated initial factor to regulate an
intermittent application of the process air to the first-stage
reactor.
16. The system of claim 15, the control system further comprising
means for introducing controlled amounts of dissolved oxygen to the
first-stage reactor.
17. The system of claim 16, the control system further comprising
means for introducing controlled amounts of a carbon source to the
second-stage reactor.
18. The system of claim 15, the one or more process parameters
further comprising wastewater flow, ammonium, ammonium-nitrogen,
ammonia, ammonia-nitrogen, nitrates, nitrate-nitrogen, nitrites,
nitrite-nitrogen, chemical oxygen demand, biochemical oxygen
demand, carbonaceous biochemical oxygen demand, dissolved oxygen,
pH, alkalinity, geometry of the first-stage reactor, and geometry
of the second-stage reactor.
19. The system of claim 16, the means for introducing controlled
amounts of dissolved oxygen comprising a process air blower.
20. The system of claim 12, the second-stage reactor further
comprising anoxic conditions for facilitating reduction of the
nitrites in the effluent to nitrogen gas.
21. The system of claim 12, the denitrified effluent exiting the
second-stage reactor comprising total phosphorous levels less than
0.3 mg/L.
Description
PRIORITY CLAIM
[0001] This application is a U.S. National stage entry under 35
U.S.C. 371 of PCT/US2011/030029 filed Mar. 25, 2011 and designating
the United States which claims the benefit of earlier filing date
and right to priority to U.S. Application No. 61/318,022 filed Mar.
26, 2010, the disclosure(s) of which is (are) expressly
incorporated by reference herein.
FIELD OF INVENTION
[0002] The present invention is in the field of wastewater
treatment, specifically, nitrogen removal from wastewater. In
particular, the invention is related to the removal of nitrogen
from a wastewater treatment system.
BACKGROUND
[0003] The presence of nitrogen compounds in lakes, rivers and
other water resources has received worldwide attention. The
presence of these nitrogen compounds in the environment is one of
the primary causes of eutrophication. It is believed that these
compounds promote unwanted growth of algae and other aquatic plants
that consume dissolved oxygen. Consequently, there is increased
demand to reduce nitrogen compounds in wastewater prior to its
discharge. It has been observed that over the past few years,
regulations for nitrogen removal by wastewater treatment plants
have become more stringent.
SUMMARY
[0004] One or more embodiments of the invention provide methods and
systems for removing nitrogen from wastewater rich in
ammonium-nitrogen.
[0005] One embodiment of the invention is a method for removing
nitrogen from wastewater rich in ammonium-nitrogen. The method
involves directing a mainstream of the wastewater to a first-stage
reactor, the first-stage reactor comprising an aerobic treatment
zone. The first-stage reactor may further comprise one or more
anoxic treatment zones.
[0006] The method further involves operating a control system for
short circuiting a conventional nitrification pathway in the
first-stage reactor. The short circuiting facilitates partial
oxidation of the ammonium-nitrogen in the mainstream to nitrites.
An effluent comprising the nitrites from the partial oxidation in
the first-stage reactor may be conveyed to a second-stage reactor
for denitrification.
[0007] The second-stage reactor may be inoculated with
heterotrophic denitrifying microorganisms. The method may further
involve maintaining anoxic conditions in the second-stage reactor
for facilitating reduction of the nitrites in the effluent to
nitrogen gas. Denitrification occurring in the second-stage reactor
may achieve total nitrogen levels substantially less than 5 mg/L.
The denitrified effluent exiting the second-stage reactor may
further comprise total phosphorous levels less than 0.3 mg/L.
[0008] The step of operating the control system may further involve
creating an environment in the aerobic treatment zone that is
conducive to short circuiting the conventional nitrification
pathway by facilitating growth of ammonia oxidizing bacteria and
inhibiting growth of nitrite oxidizing bacteria.
[0009] Moreover, operating the control system may involve
controlling levels of dissolved oxygen in the mainstream to create
the environment conducive to short circuiting. Controlling levels
of dissolved oxygen in the mainstream may involve: receiving input
values for one or more process parameters to generate at least one
set point value for the one or more process parameters, the one or
more process parameters affecting the short circuiting; calculating
an initial factor corresponding to a percent of time for
intermittently applying a fixed rate of process air to the
first-stage reactor to create the conducive environment; sampling
the mainstream to measure the one or more process parameters; and
comparing the measured process parameters against the set point
values and the calculated initial factor to regulate an
intermittent application of the process air to the first-stage
reactor. The one or more process parameters may comprise wastewater
flow, ammonium, ammonium-nitrogen, ammonia, ammonia-nitrogen,
nitrates, nitrate-nitrogen, nitrites, nitrite-nitrogen, chemical
oxygen demand, biochemical oxygen demand, carbonaceous biochemical
oxygen demand, dissolved oxygen, pH, alkalinity, geometry of the
first-stage reactor, and geometry of the second-stage reactor.
Controlling levels of dissolved oxygen in the mainstream may
further involve introducing controlled amounts of dissolved oxygen
to the first-stage reactor. Introducing controlled amounts of
dissolved oxygen may be achieved by intermittently applying a fixed
rate of process air to the first-stage reactor.
[0010] Operating the control system may further involve introducing
controlled amounts of a carbon source to the second-stage
reactor.
[0011] The method may further involve controlling pH levels in the
first-stage reactor to about 8.3. The pH level control may further
comprise introducing alkaline feedstock to the first-stage reactor
and/or recycling a denitrified effluent from the second-stage
reactor to the first-stage reactor.
[0012] Another embodiment of the invention is a system for removing
nitrogen from wastewater rich in ammonium-nitrogen. The system may
comprise a mainstream treatment system having a first-stage
reactor, a second-stage reactor, and a control system.
[0013] The first-stage reactor may comprise an aerobic treatment
zone. An environment in the aerobic treatment zone may be conducive
to short circuiting the conventional nitrification pathway by
facilitating growth of ammonia oxidizing bacteria and inhibiting
growth of nitrite oxidizing bacteria. The first-stage reactor may
further comprise one or more anoxic treatment zones.
[0014] The control system may facilitate a short circuiting of a
conventional nitrification pathway in the first-stage reactor, the
short-circuiting partially oxidizing ammonium nitrogen in the
mainstream to nitrites.
[0015] An effluent comprising nitrites may be conveyed from the
first-stage reactor to the second-stage reactor for
denitrification. The second-stage reactor may be inoculated with
heterotrophic denitrifying microorganisms and may comprise anoxic
conditions for facilitating reduction of the nitrites in the
effluent to nitrogen gas. The denitrification may achieve total
nitrogen levels substantially less than 5 mg/L. The denitrified
effluent exiting the second-stage reactor may further comprise
total phosphorous levels less than 0.3 mg/L.
[0016] The control system may comprise a processor, one or more
network interfaces for facilitating the short circuiting, and a
computer memory operatively coupled to the processor. Computer
program instructions for controlling levels of dissolved oxygen in
the mainstream to create the environment conducive to short
circuiting may be disposed within the computer memory and stored in
a non-transitory storage medium. The control system may comprise a
computer control system. The control system may further comprise a
computer program stored on a non-transitory storage medium, the
computer program including instructions configured to be executed
on the computer control system to perform a method for controlling
levels of dissolved oxygen in the mainstream to create the
environment conducive to short circuiting, the controlling
dissolved oxygen levels further comprising receiving input values
for one or more process parameters to generate at least one set
point value for the one or more process parameters, the one or more
process parameters affecting the short circuiting; calculating an
initial factor corresponding to a percent of time for
intermittently applying a fixed rate of process air to the
first-stage reactor to create the conducive environment; sampling
the mainstream to measure the one or more process parameters; and
comparing the measured process parameters against the set point
values and the calculated initial factor to regulate an
intermittent application of the process air to the first-stage
reactor.
[0017] The one or more process parameters may comprise wastewater
flow, ammonium, ammonium-nitrogen, ammonia, ammonia-nitrogen,
nitrates, nitrate-nitrogen, nitrites, nitrite-nitrogen, chemical
oxygen demand, biochemical oxygen demand, carbonaceous biochemical
oxygen demand, dissolved oxygen, pH, alkalinity, geometry of the
first-stage reactor, and geometry of the second-stage reactor.
[0018] The control system may further comprise means for
introducing controlled amounts of dissolved oxygen to the
first-stage reactor. The means for introducing controlled amounts
of dissolved oxygen may comprise a process air blower.
[0019] The control system may further comprise means for
introducing controlled amounts of a carbon source to the
second-stage reactor.
[0020] These and other embodiments of the invention are described
in detail with reference to the following drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows an illustration of a conventional
nitrification/denitrification process.
[0022] FIG. 2 shows an illustration of a conventional anammox short
cut process.
[0023] FIG. 3 shows an illustration of a short cut
nitrification/denitrification process in accordance with one or
more embodiments of the invention.
[0024] FIG. 4 shows a flowchart illustrating a method in accordance
with one or more embodiments of the invention.
[0025] FIG. 5 shows a system and process flow diagram for short cut
nitrification/denitrification in accordance with one or more
embodiments of the invention.
[0026] FIG. 6A shows a flowchart illustrating a method in
accordance with one or more embodiments of the invention.
[0027] FIG. 6B shows a flowchart illustrating a method in
accordance with one or more embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] FIG. 1 represents a conventional process for removal of
nitrogen from wastewater. As shown, this involves nitrification
followed by denitrification. During nitrification, ammonia/nitrogen
compounds in the wastewater are first oxidized into nitrites. This
oxidation is performed by ammonia oxidizing bacteria (AOB) in the
presence of dissolved oxygen. Ammonia oxidizing bacteria typically
belong to the genus Nitrosomonas. The nitrite is then further
oxidized into nitrate. This is primarily done by nitrite oxidizing
bacteria (NOB) bacteria of the genus Nitrobacter. Nitrobacter is
often found in tandem with Nitrosomonas since the end product of
Nitrosomonas metabolism provides the energy substrate for
Nitrobacter. Denitrification involves the reduction of the nitrate
to nitrogen gas through a series of intermediate gaseous nitrogen
oxide products. Denitrification is carried out in an anaerobic or
anoxic environment, typically in the presence of bacteria requiring
an external carbon source.
[0029] These conventional processes may involve high costs,
primarily due to the aeration requirements, that is, bringing and
introducing oxygen into the wastewater treatment plant for the
nitrification reaction, and the addition of an external or
supplemental carbon source (typically, methanol) for facilitation
of the denitrification reaction. The supplemental carbon expense
may represent as much as 80-90% of operating costs of
denitrification. There is increasing pressure to reduce operating
costs associated with supplemental carbon and process air
requirements.
[0030] Processes have been developed to short-circuit the
above-described nitrification/denitrification biological pathway
via nitrite (NO2) which is a common intermediate product for both
nitrification and denitrification. The terms "short-circuit" and
"short cut" are used interchangeably herein. Referring to FIG. 2,
these short-circuit processes involve initially producing an
ammonium-nitrite mixture by converting the ammonium to nitrite in a
single reactor using 50% of the oxygen for conventional processes.
As seen in FIG. 2, this may result in a 63% overall reduction in
dissolved oxygen requirements. The ammonium-nitrite mixture may be
then converted under anoxic or anaerobic conditions to nitrogen gas
with ammonium as the electron donor. The reaction relies on
anammox, a slow-growing autotrophic bacteria, for catalyzing the
reaction and facilitating the conversion to nitrogen. This process
is carried out without addition of external or supplemental carbon
sources.
[0031] These processes are sidestream recycle processes, that is,
they are used to treat or process effluent/fluids obtained by
dewatering of the sludge generated during the wastewater treatment
cycle. Most of these processes use suspended growth systems, that
is, they use microorganisms and bacteria suspended in the
wastewater being treated. These processes are used to treat
high-strength ammonium wastes (i.e., centrate from anaerobic
digester sludge treatment), and they rely on anammox bacteria for
the denitrification reaction. Moreover, these processes typically
involve heat input and batch processing. Existing short-circuit
processes typically achieve 80-90% nitrogen removal when applied to
high-strength ammonium wastewater (typically about 1,000 mg/L
ammonium-nitrogen). The resulting effluent still contains 100-200
mg/L nitrogen. Thus, further treatment, including discharging the
treated effluent to the mainstream for additional nitrogen removal,
may typically be required to achieve target nitrogen level
reductions if the wastewater treatment plant is subject to
stringent nitrogen discharge limits.
[0032] Although anammox bacteria is attractive because of its
reduction or elimination of the need for supplemental carbon, it is
notorious for long startup periods (approximately one year),
toxicity issues, nitrite-limitation issues for single-stage
applications, and effluent nitrate (NO3-N) production of about
10-12% of influent nitrogen. While these aspects might be
manageable for a sidestream process, the same would not hold for
mainstream processes subject to stringent nutrient effluent
limits.
[0033] Referring now to FIG. 3, one or more embodiments of the
present invention comprise methods and systems for the removal of
nitrogen from wastewater by short-circuiting the nitrification
pathway using the intermediary nitrite, which is common to both
nitrification and denitrification reactions. In one or more
embodiments of the invention, at least one aerobic biofilter is
paired with at least one anoxic biofilter under unique operating
conditions. Exemplary processes and apparatus for nitrification and
denitrification have been disclosed in U.S. Pat. Nos. 5,776,344 to
McCarty et al. and in 7,396,466 to Bonazza et al. The contents of
these referenced patents are incorporated herein by reference in
their entirety. Furthermore, where a definition or use of a term in
a reference, which is incorporated by reference herein is
inconsistent or contrary to the definition of that term provided
herein, the definition of that term provided herein applies and the
definition of that term in the reference does not apply.
[0034] The methods of the invention may involve treatment of
mainstream, as opposed to sidestream, wastewater treatment. One or
more embodiments of the invention may result in lower energy
requirements and supplemental carbon needs compared to those for
conventional nitrification/denitrification.
[0035] Referring now to FIG. 4, in one or more embodiments of the
invention, the wastewater may be initially passed through an
aerobic biofilter used as a first-stage reactor 404. The
first-stage reactor may be under aerobic and controlled operating
conditions. The first-stage aerobic reactor comprises granular
media and a biological fixed-film or biofilm on the media. AOB may
be active on the outer layers of the biofilm. This outer layer may
be in direct contact with the wastewater comprising dissolved
oxygen. This promotes conversion of ammonia and nitrogen compounds
in the wastewater to nitrites 408. The first-stage reactor may
accomplish partial nitrification (nitritation) and simultaneous
nitrification/denitrification (SND) at low dissolved oxygen
conditions. The effluent comprising the nitrites is then conveyed
to an anoxic biofilter used as a second-stage reactor 412. The
second-stage reactor may be under anoxic conditions. The
second-stage reactor comprises granular media and a biological
fixed-film or biofilm on the media. The biofilm on the second-stage
reactor is inoculated with heterotrophic bacteria. Heterotrophic
bacteria reduce the nitrites to gaseous nitrogen 416, including
elemental nitrogen, which may then be purged or expelled from the
wastewater 420.
[0036] The embodiments of the system of the invention occupy a
smaller footprint as compared to conventional
nitrification/denitrification systems, making it applicable for
sites with limited space, and especially those that must retrofit
to meet more stringent nitrogen discharge limits.
[0037] The embodiments of the invention utilize a fixed-film
approach unlike the suspended growth systems of the conventional
short cut processes. In fixed film systems, the nitrifying and
denitrifying bacteria and other microorganisms exist and grow on a
fixed support structure. The fixed film processes are inherently
stable and resistant to organic and hydraulic shock loadings.
[0038] The denitrification reaction may be carried out by proven
heterotrophic bacteria, as opposed to denitrification using
autotrophic anammox bacteria as used in conventional short cut
processes. Heterotrophic bacteria require an external organic
carbon source to obtain their energy and nutrition. In direct
contrast, an autotroph is an organism able to make its own food.
Autotrophic organisms take inorganic substances into their bodies
and transform them into organic matter. However, autotrophs, such
as anammox bacteria, have long start-ups, slow recovery after
upset, and often require supplemental heat to compensate for slow
growth. As used herein, the term "anoxic" means the absence of free
dissolved oxygen, in contrast with "anaerobic" which means the
absence of oxygen including chemically bound oxygen.
[0039] One or more embodiments of the present invention may result
in significant reductions in the required oxygen to be transferred
for oxidation and also in the amount of carbon addition required
for bacterial growth in denitrification. Since the oxidation of
ammonia is only taken to nitrite, and nitrite is reduced instead of
being taken to nitrate and then having the nitrate reduced, there
may be a 25% reduction in oxygen requirements and a 40% reduction
in carbon requirements.
[0040] FIG. 5 depicts a system and process flow diagram for
carrying out a method in accordance with one or more embodiments of
the invention. The system 500 comprises a first-stage aerobic
reactor 512 and a second-stage anoxic reactor 532. The first-stage
aerobic reactor 512 and the second-stage anoxic reactor 532 may
include a biologically active material (not shown). The
biologically active material broadly includes any microorganism
affixed to a solid support (not shown) that is capable of
accomplishing the desired nitrification or denitrification. The
material may be in the form of a fixed film, which is herein
defined as microorganisms that grow in a film on a support
structure. In the one or more embodiments of the invention, the
support structure may comprise granular media 514, 534 packed in
one or more substantially horizontal layers 514a, 534a. As shown in
FIG. 5, the first-stage reactor 512 and the second-stage reactor
532 each may comprise a single monomedia. However, multiple layers
may be used in other embodiments. Multiple layers in a single
reactor may be stacked vertically. Different layers may comprise
different types and/or sizes of support structures. The support
structure may include granular media 514, 534 such as silica sand,
a plastic media such as plastic beads, one or more sheets (not
shown) such as plastic sheets, or some other support such as
rotating biological contactors (not shown). The biologically active
material may comprise a biologically active filter or biofilter.
For example, the filter may include granular media 514, 534
configured in a packed bed reactor 512, 532 and inoculated with
microorganisms, having a porosity of less than about 80%. In other
embodiments, the porosity may be less than about 60%. In yet other
embodiments, the porosity may be less than about 40%. The aerobic
biofilter 512 may be inoculated with the nitrifying bacteria, such
as AOB, while the anoxic biofilter 532 may be inoculated with
heterotrophic bacteria.
[0041] The AOB may be grown on the support by passing wastewater
through the biologically active material and controlling conditions
under which AOB may grow while creating conditions necessary to
reduce or eliminate the NOB. Growth of AOB may be affected by many
factors, including, but not limited to, dissolved oxygen, pH,
alkalinity, nitrogen loading, BOD loading, trace nutrients,
temperature, reaction time, and hydraulic shear related to
hydraulic loading of the first-stage reactor.
[0042] As described earlier, the first-stage aerobic reactor 512
comprises a biofilm. While AOB is active on the outer layers of
this biofilm because it is in contact with oxygen-rich wastewater,
the deeper layers of the biofilm may have limited to non-existent
access to dissolved oxygen. These conditions promote growth of
anammox and heterotrophic bacteria. These denitrifying bacteria may
further affect some level of nitrogen removal depending on
diffusion and wastewater characteristics. As mentioned earlier, the
amount of dissolved oxygen provided to the first-stage aerobic
reactor 512 may also be limited or controlled. This also promotes
the growth of anammox or heterotrophic bacteria in the deeper
layers of the biofilm. The denitrifying bacteria may convert some
of the nitrite produced in the outer layers of the biofilm to
nitrogen gas. While this denitrification may constitute a bonus or
an added advantage, target denitrification levels may be achieved
by conveying an effluent 536 comprising nitrites from the
first-stage aerobic reactor 512 to the second-stage anoxic reactor
532. In the second-stage anoxic reactor 532, heterotrophic bacteria
promote denitrification in a proven and controllable manner.
[0043] In yet another embodiment, both nitrification and
denitrification may be carried out in a single reactor 512 having
process air (dissolved oxygen) applied at a location within the
granular media 514. This may affect both an outer aerobic layer and
an inner anoxic layer. Such a reaction may be carried out in an
upflow mode with the effluent being recycled for optimal nitrogen
removal.
[0044] In the second-stage reactor 532, anoxic or similar
conditions may be maintained to facilitate reduction of the
nitrites to nitrogen. In the one or more embodiments of the
invention, denitrification may be carried out using a deep bed
fixed-film biological denitrification reactor to provide total
nitrogen (TN) and total phosphorous (TP) removal. The
denitrification reactor 532 may be used as the final treatment step
in the TN and TP removal processes to help a wastewater treatment
facility meet stringent TN and TP effluent limits. Effluent limits
for TN and TP may be less than 1-10 mg/L and less than 0.1-2 mg/L,
respectively. In one or more embodiments, effluent limits for TN
and TP may be less than 5 mg/L and less than 0.3 mg/L, respectively
These effluent limits are substantially lower than the quality of
effluent from sidestream processes (e.g., 100-200 mg/L TN), for
which existing short-circuit processes are designed.
[0045] Specially sized and shaped granular media 534 may be used in
the second-stage reactor 532. The media functions as a support
medium for denitrifying heterotrophic bacteria and the deep bed
environment is conducive to efficient reduction of nitrite to
nitrogen gas and solids removal. The contact between wastewater and
biomass is facilitated and hydraulic short-circuiting is negligible
even during plant upsets.
[0046] The media within the first-stage reactor 512 and/or the
second-stage reactor 532 may further allow for heavy capture of
solids of at least 1.0 pound of solids per square foot of filter
surface area before backwashing may be required.
[0047] Conventional heterotrophic bacteria may exist as a
fixed-film on the second-stage anoxic reactor 532. The
heterotrophic bacteria convert the nitrites to nitrogen gas in the
presence of an external carbon source, which may be stored in a
carbon source tank 552. The carbon source feeds the heterotrophic
microorganisms or bacteria. Examples of carbon sources capable of
working with microorganisms within the filter unit for
denitrification are methanol, ethanol, glycerine, acetic acid,
brewery wastes, sugars, primary effluent, and combinations of
these. The carbon source may be introduced in a controlled manner
using automated means. The automated means may also be used
simultaneously for auto dosing of metal salts for ortho phosphate
removal.
[0048] The second-stage denitrification reactor 532 may employ a
"bump" operation to remove or purge accumulated gas--nitrogen or
CO.sub.2--that can build up in the biofilter media 534. If desired,
this bumping can be accomplished without removing the second-stage
reactor 532 from service by applying backwash water to the bottom
of the biofilter, releasing the entrapped gas into the atmosphere
and reducing headloss.
[0049] Since the one or more embodiments of the invention comprise
mainstream wastewater treatment, tighter control on nitrogen and
phosphorous levels in the effluent may be required. Effluent limits
of less than 5 mg/L TN and less than 0.3 mg/L TP may be achieved by
embodiments of the methods and systems of the present invention.
This is in contrast to existing short-circuit processes, which
typically achieve 80-90% nitrogen removal when applied to
high-strength ammonium wastewater (typically about 1,000 mg/L
ammonium-nitrogen), resulting in an effluent that still contains
100-200 mg/L nitrogen. Thus, the existing short-circuit processes
may require further treatment, including discharging the treated
effluent to the mainstream for additional nitrogen removal, to
achieve target nitrogen level reductions if the wastewater
treatment plant is subject to stringent nitrogen discharge
limits.
[0050] One or more embodiments of the invention involve controlling
one or more process parameters during the passage of the wastewater
through the first-stage fixed-film biological reactor 512 in order
to create an environment conducive to the growth of ammonia
oxidizing bacteria (AOB) while inhibiting the growth of nitrite
oxidizing bacteria (NOB). Thus, optimal conditions would maximize
AOB while substantially reducing or eliminating NOB.
[0051] In accordance with one or more embodiments of the invention,
NOB may be inhibited by controlling the concentration of dissolved
oxygen within the first-stage reactor 512. The dissolved oxygen
concentration may be controlled "indirectly," i.e., by measuring
process parameters other than dissolved oxygen concentration, and
using the measured process parameters as feedback in a control
system.
[0052] The system 500 may further comprise a wastewater source 556,
a feed tank 560, a feed pump 564, an influent mainstream of
wastewater 504, a clearwell 568, and a control system 506. The
control system 506 further comprises a flow meter 528, an influent
sampler 508, an intermediate sampler 540, an effluent sampler 552,
an analyzer 516, the process air blower 524, a carbon feed pump
544, and a controller 520.
[0053] Wastewater from a wastewater source 556 may be supplied to
the feed tank 560. To transport the wastewater from the wastewater
source 556 to the feed tank 560, a sump pump (not shown), a pumping
station (not shown), or flow by gravity (not shown), among other
things, may be used in one or more embodiments. The feed pump 564
may pump the wastewater in the feed tank 560 as the mainstream of
influent wastewater 504 to the first-stage reactor 512. The
mainstream of influent wastewater 504 may contain nitrogen
compounds, such as ammonium-nitrogen (NH4-N). Samples of the
influent wastewater 504 may be collected by the influent sampler
508 prior to the influent wastewater 504 entering the first-stage
nitrification reactor 512. The influent sampler 508 may be in
communication with the analyzer 516. The analyzer 516 may be used
to determine various process parameters, such as concentrations of
ammonium (NH4), ammonium-nitrogen (NH4-N), ammonia (NH3),
ammonia-nitrogen (NH3-N), nitrates (NO3), nitrate-nitrogen (NO3-N),
nitrites (NO2), and nitrite-nitrogen (NO2-N), in the influent
wastewater 504 based on the sample collected by the influent
sampler 508. In one or more embodiments, the analyzer 516 may
comprise an instrument that can detect chemical substances that
absorb light in the ultraviolet or visible wavelength range.
[0054] The flow meter 528 may be disposed along the flow path of
mainstream influent wastewater stream 504, upstream from the
first-stage reactor 512. The flow meter 528 may be used to measure
the flow rate of the influent wastewater 504.
[0055] The controller 520 may comprise a programmable logic
controller (PLC) (not shown) and a human-machine interface (HMI)
(not shown). The HMI may allow an operator to enter one or more
predetermined set point values of one or more process parameters
that the PLC may control using computer program instructions. The
controller 520 may further comprise a processor (not shown); one or
more network interfaces (not shown); and a computer memory (not
shown). The computer memory may have disposed within it computer
program instructions (not shown) for controlling levels of
dissolved oxygen in the mainstream to create conditions conducive
to short circuiting a conventional nitrification pathway in the
first-stage reactor 512, including, but not limited to: computer
program instructions for receiving input values for one or more
process parameters to generate at least one set point value for the
one or more process parameters; computer program instructions for
calculating an initial factor corresponding to a percent of time
for intermittently applying a fixed rate of process air to the
first-stage reactor 512; computer program instructions for
accepting measurements of the one or more process parameters
received from sampling the mainstream; and computer program
instructions for comparing the measured process parameters against
the set point values and the calculated initial factor to regulate
an intermittent application of process air to the first-stage
reactor 512.
[0056] The controller 520 may receive one or more input values and
determine an initial percent aeration factor (PAF), i.e., an
initial factor corresponding to a percent of time that a fixed rate
of process air is to be intermittently applied to the first-stage
reactor 512. The factor may be used to achieve optimal AOB growth
promotion and NOB growth inhibition based on computer program
instructions. A minimum fixed rate of process air to be applied to
the first-stage reactor 512 of substantially at least 0.8 icfm/sf
may be required to ensure even distribution of the process air
within the first-stage reactor 512.
[0057] Process parameters on which a factor determination may be
based include wastewater flow, ammonium (NH4), ammonium-nitrogen
(NH4-N), ammonia (NH3), ammonia-nitrogen (NH3-N), nitrates (NO3),
nitrate-nitrogen (NO3-N), nitrites (NO2), and nitrite-nitrogen
(NO2-N), chemical oxygen demand (COD), biochemical oxygen demand
(BOD), carbonaceous biochemical oxygen demand (cBOD), dissolved
oxygen, pH, alkalinity, geometry of the first-stage reactor 512,
and geometry of the second-stage reactor 532. The foregoing list of
process parameters is not exhaustive. Any process parameter
suitable for determining a factor that will achieve optimal AOB
growth promotion and NOB growth inhibition may be used.
[0058] The controller 520 may regulate a process air blower 524
based on the factor determination. The process air blower 524 may
intermittently supply dissolved oxygen into the first-stage reactor
512 such that conditions are created to optimize the growth of AOB
and inhibit the growth of NOB within the first-stage reactor 512,
which short cuts nitrification/denitrification as described
previously with reference to FIG. 3. For example, a calculated
factor of 50% may be implemented as 30 minutes of aeration in an
hour followed by 30 minutes of no aeration, or 15 minutes of
aeration in a 30 minute period followed by 15 minutes of no
aeration. A unit period of time may be defined, and the factor may
be applied to the unit period to control the frequency and duration
of operation of the process air blower 524.
[0059] The analyzer 516 and the flow meter 528 may be in
communication with and provide input values (corresponding to
process parameters) to the controller 520.
[0060] Upon receiving the collected sample of influent wastewater
504 from the influent sampler 508, the analyzer 516 may analyze the
influent wastewater 504 sample to determine its NH4-N
concentration. The analyzer 516 may then relay the determined NH4-N
concentration to the controller 520. In one or more embodiments of
the invention, the controller 520 may determine an initial factor
based on the NH4-N concentration and the measured flow rate of the
mainstream influent wastewater 504.
[0061] The influent wastewater 504 may flow through the first-stage
reactor 512 where the AOB oxidizes the nitrogen compounds, such as
ammonium, to nitrites. In one or more embodiments of the invention,
the influent wastewater 504 may flow through the first-stage
reactor 512 in an upward direction (upflow). However, the influent
wastewater 504 may flow through the first-stage reactor 512 in a
downward direction (downflow) in other embodiments. The substantial
or complete absence of NOB prevents the further oxidation of
nitrites to nitrates. A stream of first-stage reactor effluent 536
may flow from the first-stage reactor 512 to a second-stage
denitrification reactor 532, the second-stage reactor disposed
downstream from the first-stage reactor 512.
[0062] An intermediate sampler 540 may collect samples of the
stream of first-stage reactor effluent 536 prior to the stream 536
entering the second-stage reactor 532. The intermediate sampler 540
may be in communication with the analyzer 516. The analyzer 516 may
be used to determine the concentrations of various process
parameters, such as NH4-N, NO3-N, and NO2-N, in the influent
wastewater 504 based on the sample collected by the intermediate
sampler 540. The analyzer 516 communicates this information to the
controller 520, which in turn uses the determined concentration of
each of NH4-N, NO3-N and NO2-N as input values for adjusting its
factor determination. For example, a predetermined set point value
may be a concentration of NH4-N of approximately 1 mg/L. If the
NH4-N concentration of the sample collected by the intermediate
sampler 540 is greater than this set point value of approximately 1
mg/L NH4-N concentration, then the factor may be adjusted upward (a
higher percentage) as the NH4-N concentration indicates that not
enough process air is being applied within the first-stage reactor
512, i.e., not enough of the wastewater ammonium is being oxidized.
Similarly, a predetermined set point value may be a concentration
of NO3-N of approximately 1 mg/L. If the NO3-N concentration of the
sample collected by the intermediate sampler 540 is greater than
this set point value of approximately 1 mg/L NO3-N concentration,
then the factor may be adjusted downward (a lower percentage) as
the NO3-N concentration indicates that too much process air is
being applied within the first stage reactor 512, i.e., the
abundance of process air is creating conditions in which NOB growth
is not being sufficiently inhibited and thus nitrites are being
oxidized to nitrates. Other process parameters, such as dissolved
oxygen concentration and pH may also be measured and factored into
the factor calculation as tertiary levels of control.
[0063] As the stream of first-stage reactor effluent 536 flows
through the second-stage reactor 532, the heterotrophic bacteria
reduce the nitrites in the stream 536 to nitrogen gas. The nitrogen
gas may be purged or expelled from the stream 536. An effluent
stream 548 exits the second-stage reactor and into the clearwell
568. The effluent stream 548 stored in the clearwell 568 may
undergo further treatment.
[0064] An effluent sampler 552 may collect samples of the effluent
stream 548. The effluent sampler 552 may be in communication with
the analyzer 516. The analyzer 516 may be used to determine the
concentrations of various process parameters, such as NH4-N, NO3-N,
and NO2-N, in the effluent stream 548 based on the sample collected
by the effluent sampler 552. The analyzer 516 communicates this
information to the controller 520, which in turn uses the
determined concentration of each of NH4-N, NO3-N and NO2-N as input
values for further adjusting its factor determination. The
controller 520 may also use these process parameters to regulate a
carbon feed pump 544 that supplies a carbon source from the carbon
source tank 552 to the second-stage reactor 532. The heterotrophic
microorganisms or bacteria use the carbon as its energy source for
growth.
[0065] FIG. 6A shows a flow chart illustrating a method of
operating a control system to control levels of dissolved oxygen in
the mainstream in accordance with one or more embodiments of the
invention. Controlling levels of dissolved oxygen in the mainstream
creates an environment conducive to short circuiting a conventional
nitrification pathway in the first-stage reactor.
[0066] The method of operating the control system may involve
receiving input values for one or more process parameters 602.
These input values may be entered into the control system by an
operator using a human-machine interface (HMI) and received by a
programmable logic controller (PLC) in communication with the
HMI.
[0067] One or more process parameters may be measured 604 in order
to calculate an initial factor corresponding to a percent of time
for intermittently applying a fixed rate of process air to the
first-stage reactor 606. A fixed rate of process air may be applied
to the reactor based on the calculated factor 608 in order to
create the environment conducive to short circuiting a conventional
nitrification pathway in the first-stage reactor (i.e., facilitate
growth of ammonia oxidizing bacteria and inhibiting growth of
nitrite oxidizing bacteria).
[0068] The process parameters may be measured periodically 610 in
order to recalculate the aforementioned factor 612 that corresponds
to a percent of time for intermittently applying a fixed rate of
process air to the first-stage reactor. Alternatively, one or more
of the process parameters may be continually measured rather than
periodically measured. The recalculated factor 612 may be different
than the initially calculated factor 606. If so, an adjusted fixed
rate of process air may be applied 614. An increase in the
recalculated factor 612 relative to the initially calculated factor
606 may correspond with an increase in the percent of time for
intermittently applying a fixed rate of process air to the
first-stage reactor. A decrease in the recalculated factor 612
relative to the initially calculated factor 606 may correspond with
a decrease in the percent of time for intermittently applying a
fixed rate of process air to the first-stage reactor.
[0069] In this manner, the control system may employ a feedback
loop, measuring process parameters 610 and adjusting the percent of
time for intermittently applying a fixed rate of process air to the
first-stage reactor 614. This allows for controlling levels of
dissolved oxygen in the mainstream, which creates an environment
conducive to short circuiting a conventional nitrification pathway
in the first-stage reactor (i.e., facilitate growth of ammonia
oxidizing bacteria and inhibiting growth of nitrite oxidizing
bacteria).
[0070] FIG. 6B shows a flow chart illustrating a method of
operating a control system to control levels of a carbon source in
the second-stage reactor.
[0071] The method of operating the control system may involve
receiving input values for one or more process parameters 620.
These input values may be entered into the control system by an
operator using a human-machine interface (HMI) and received by a
programmable logic controller (PLC) in communication with the
HMI.
[0072] One or more process parameters may be measured 622 in order
to determine an amount of a carbon source to introduce to the
second-stage reactor 624. An amount of carbon may be introduced to
the second-stage reactor 626 based on the determination 624.
[0073] The process parameters may be measured periodically 628 in
order to determine whether the amount of carbon source introduced
to the second-stage reactor should be adjusted 632. Alternatively,
one or more of the process parameters may be continually measured
rather than periodically measured.
[0074] In this manner, the control system may employ a feedback
loop, measuring process parameters 628 and adjusting the amount of
carbon introduced to the second-stage reactor 632. This allows for
controlling levels of a carbon source in the second-stage
reactor.
[0075] Referring back to FIG. 5, in accordance with one or more
embodiments of the invention, NOB is inhibited by adjusting the pH
of the influent wastewater 504 within the first-stage reactor 512.
The AOB existing on the outer layers of the biofilm act on the
ammonia/nitrogen compounds to oxidize these compounds to nitrites.
In one embodiment of the invention, the pH of the first-stage
aerobic reactor 512 is maintained at about 8.3. Growth rate of
nitrite NOB, responsible for converting nitrites to nitrates, may
be eight times higher at a pH of 7 compared to at a pH of about 8.
However, the growth rate of the AOB may change negligibly in this
pH range. Operating at a pH of about 8.3 may favor the desired AOB
and inhibit the undesirable NOB, thereby promoting conversion of
ammonia to nitrite, while suppressing oxidation of nitrite to
nitrate. The higher pH may further affect the available form of
ammonium/ammonia, creating more available in the ammonia (NH3)
form, which may also inhibit the growth of NOB. Other process
parameters that may be controlled to create an environment
conducive to substantially reducing or eliminating NOB include, but
are not limited to, oxidation-reduction potential (ORP), Oxygen
Uptake Rate (OUR), ammonium-nitrogen (NH4-N), free ammonia (FA),
free nitrous acid (FNA), temperature, salinity, and sludge age.
[0076] Feedstock comprising sodium bicarbonate, sodium hydroxide,
or magnesium hydroxide may be used to adjust the pH or to add
alkalinity. However, any chemical compound suitable for adjusting
the pH or adding alkalinity may be used. In yet another embodiment,
the effluent from the second-stage anoxic/denitrification reactor
532 may be recycled for further nitrogen removal and to balance
alkalinity in the system. The alkalinity may also assist in
controlling the pH to about 8.3.
[0077] The use of a fixed-film biofilm reactor instead of a
suspended-growth system may also inhibit NOB. AOB may exist on the
outer parts of the biofilm while NOB may exist deeper within the
biofilm where oxygen is limited. The half saturation constant, Ks,
is 0.3 mg/L for AOB and 1.1 mg/L for NOB, which may further work to
inhibit NOB (lower saturation constants show more affinity for
oxygen).
[0078] Although not illustrated in FIG. 5, it is to be understood
that various combinations of effluent recycling may be done to
further effectuate nitrification/denitrification in accordance with
one or more embodiments of the invention. For example, the
first-stage reactor effluent 536 and/or the second-stage effluent
stream 548 may be recycled back through the first-stage reactor
512. Another recycle process may involve recycling the second-stage
effluent stream 548 back through the second stage reactor 532.
Chemical addition to adjust pH and supplement alkalinity is also
not illustrated in FIG. 5. Furthermore, one or more embodiments of
the invention may comprise multiple first-stage nitrification
reactors 512 and/or second-stage nitrification reactors 532 in
series or in parallel or a combination thereof.
[0079] Exemplary methods and systems for removing nitrogen from
wastewater rich in ammonium-nitrogen according to embodiments of
the present invention are described with reference to the
accompanying drawings. The terminology used herein is for the
purpose of describing particular embodiments only and is not
intended to be limiting of the invention. As used herein, the
singular forms "a", "an", and "the" are intended to include the
plural forms as well, unless the context clearly indicates
otherwise. It will be further understood that the terms "comprises"
and/or "comprising," when used in this specification, specify the
presence of stated features, integers, steps, operations, elements,
and/or components, but do not preclude the presence or addition of
one or more other features, integers, steps, operations, elements,
components, and/or groups thereof.
[0080] The corresponding structures, components, acts, and
equivalents of all means or step plus function elements in the
claims below are intended to include any structure, material or act
for performing the function in combination with other claimed
elements as specifically claimed. The description of the present
invention has been presented for purposes of illustration and
description, but is not intended to be exhaustive or limited to the
invention in the form disclosed. Many modifications and variations
will be apparent to those of ordinary skill in the art. The
embodiment was chosen and described in order to best explain the
principles of the invention and the practical application, and to
enable others of ordinary skill in the art to understand the
invention for various embodiments with various modifications as are
suited to the particular use contemplated.
[0081] Aspects of the present invention may take the form of an
entirely hardware embodiment, an entirely software embodiment
(including firmware, resident software, micro-code, etc.) or an
embodiment combining software and hardware aspects that may all
generally be referred to herein as a "circuit," "module" or
"system." Furthermore, aspects of the present invention may take
the form of a computer program product embodied in one or more
non-transitory computer readable medium(s) having computer readable
program code embodied thereon.
[0082] Any combination of one or more computer readable medium(s)
may be utilized. The computer readable medium may be a computer
readable storage medium. A computer readable storage medium may be,
for example, but not limited to, an electronic, magnetic, optical,
electromagnetic, infrared, or semiconductor system, apparatus, or
device, or any suitable combination of the foregoing. More specific
examples (a non-exhaustive list) of the computer readable storage
medium would include the following: an electrical connection having
one or more wires, a portable computer diskette, a hard disk, a
random access memory (RAM), a read-only memory (ROM), an erasable
programmable read-only memory (EPROM or Flash memory), an optical
fiber, a portable compact disc read-only memory (CD-ROM), an
optical storage device, a magnetic storage device, or any suitable
combination of the foregoing. In the context of this document, a
computer readable storage medium may be any tangible medium that
can contain, or store a program for use by or in connection with an
instruction execution system, apparatus, or device.
[0083] Program code embodied on a non-transitory computer readable
medium may be transmitted using any appropriate medium, including
but not limited to wireless, wireline, optical fiber cable, RF,
etc., or any suitable combination of the foregoing.
[0084] Computer program code for carrying out operations for
aspects of the present invention may be written in any combination
of one or more programming languages, including an object oriented
programming language such as Java, Smalltalk, C++ or the like and
conventional procedural programming languages, such as the "C"
programming language or similar programming languages.
[0085] Aspects of the present invention are described below with
reference to flowchart illustrations and/or block diagrams of
methods, apparatus (systems) according to embodiments of the
invention. It will be understood that each block of the flowchart
illustrations and/or block diagrams, and combinations of blocks in
the flowchart illustrations and/or block diagrams, can be
implemented by computer program instructions. These computer
program instructions may be provided to a processor of a general
purpose computer, special purpose computer, or other programmable
data processing apparatus to produce a machine, such that the
instructions, which execute via the processor of the computer or
other programmable data processing apparatus, create means for
implementing the functions/acts specified in the flowchart and/or
block diagram block or blocks.
[0086] These computer program instructions may also be stored in a
non-transitory computer readable medium that can direct a computer,
other programmable data processing apparatus, or other devices to
function in a particular manner, such that the instructions stored
in the computer readable medium produce an article of manufacture
including instructions which implement the function/act specified
in the flowchart and/or block diagram block or blocks.
[0087] The computer program instructions may also be loaded onto a
computer, other programmable data processing apparatus, or other
devices to cause a series of operational steps to be performed on
the computer, other programmable apparatus or other devices to
produce a computer implemented process such that the instructions
which execute on the computer or other programmable apparatus
provide processes for implementing the functions/acts specified in
the flowchart and/or block diagram block or blocks.
[0088] It is to be understood that the invention is not to be
limited or restricted to the specific examples or embodiments
described herein, which are intended to assist a person skilled in
the art in practicing the invention. Although the invention is
preferably directed to the removal of nitrogen compounds from
wastewater, it is not necessarily limited to such applications. For
example, the invention may also be used to reduce phosphorus
contaminants or BOD pollutants in wastewater. The invention may
also be applied to large scale treatment facilities or industrial
applications. Accordingly, numerous changes may be made to the
details of procedures for accomplishing the desired results. These
and other similar modifications will readily suggest themselves to
those skilled in the art, and are intended to be encompassed within
the spirit of the present invention disclosed herein and the scope
of the appended claims.
* * * * *